When atoms share more than one pair of electrons they form multiple bonds. This dramatically affects bond strength and bond length.
| Bond Type | Shared Pairs | Example | Bond Length | Bond Enthalpy |
|---|---|---|---|---|
| Single (C–C) | 1 | Ethane C₂H₆ | 154 pm | 346 kJ mol⁻¹ |
| Double (C=C) | 2 | Ethene C₂H₄ | 134 pm | 614 kJ mol⁻¹ |
| Triple (C≡C) | 3 | Ethyne C₂H₂ | 120 pm | 839 kJ mol⁻¹ |
📏 Bond Length
As bond order increases, bond length decreases. More shared electron density pulls the nuclei closer together.
💪 Bond Strength
As bond order increases, bond enthalpy increases. More shared electrons = stronger electrostatic attraction to both nuclei.
🔑 The Key Relationship
Bond order ↑ → Bond length ↓ → Bond strength ↑
This is an inverse relationship between length and strength that appears frequently in Paper 1 multiple-choice questions.
⚠️ Examiner Trap
A double bond is not twice as strong as a single bond. The second pair of electrons (pi bond) overlaps laterally, which is less effective than the first (sigma bond). Similarly, a triple bond is not three times as strong.